High velocity linear induction launchers

Electromagnetic launchers (EMLs) have received great attention in the last decades because of their potential application to a variety of energy, transportation, space, and defense systems. Particularly, they can serve as kinetic weapons, such as ground-based and naval artillery, space-based anti-missile guns, Earth-to-Orbit launcher, and mass transportation. The main advantage is that EMLs can accelerate projectiles to hyper velocities, i.e. velocities greater than those achievable with conventional cannons. The Linear Induction Launcher (LIL) is an air-cored electromagnetic coil launcher operating on the principle of the induction motor. Polyphase excitation of the coils constituting the barrel is designed to create an electromagnetic wave packet, which travels with increasing velocity from the breech to the muzzle. The projectile is a hollow conducting cylinder (sleeve) carrying the payload within it. Relative motion (slip) of the wave packet with respect to the projectile induces azimuthal currents in the sleeve that interacts with the exciting magnetic field to produce both propulsive and centering forces. This paper deals with the design of a high velocity linear induction launcher with muzzle velocity up to 6000 m/s. It addresses the design specifications of the launcher and utilizing a projectile weighing 1 kg. In the paper, the design specifications with simulation results for the phase voltages, the currents, the velocity, and the temperature rise of the sleeve are presented.     

Penetration scaling in atomistic simulations of hypervelocity impact

We present atomistic molecular dynamics simulations of the impact of copper nano particles at 5 km s⁻¹ on copper films ranging in thickness from from 0.5 to 4 times the projectile diameter. We access both penetration and cratering regimes with final cratering morphologies showing considerable similarity to experimental impacts on both micron and millimetre scales. Both craters and holes are formed from a molten region, with relatively low defect densities remaining after cooling and recrystallisation. Crater diameter and penetration limits are compared to analytical scaling models: in agreement with some models we find the onset of penetration occurs for 1.0 < f/d_p < 1.5, where f is the film thickness and d_p is the projectile diameter. However, our results for the hole size agree well with scaling laws based on macroscopic experiments providing enhanced strength of a nano-film that melts completely at the impact region is taken into account.     

Stress analysis of the rails of a new high velocity armature design in an electromagnetic launcher

In an electromagnetic launcher, the magnetic field creates a dynamic force that moves the armature forward. In an electromagnetic launcher, the armature reaches a critical velocity during the launch which causes high amplitude stress and strain. In addition, high stress and strain damage the rails and reduces its life span. The purpose of this paper is to investigate the effect of armature velocity as well as the rails physical and geometrical properties on the dynamic response of the rails in an electromagnetic launcher. In this study the second moment of inertia of the rails cross-section, Young modulus, foundation stiffness and density of the rails are constant in location and time. In our formulation of governing non-linear differential equations, Maxwell equations and deflection equation are applied to the rails under dynamic loading. To solve the non-linear governing differential equations a finite difference method is utilized.     

Critical Velocities in Two-Component Superfluid Bose Gases

On the ground of the Landau criterion we study the behavior of critical velocities in a superfluid two-component Bose gas. It is found that under motion of the components with different velocities the velocity of each component should not be lower than a minimum phase velocity of elementary excitations (s ₋). The Landau criterion yields a relation between the critical velocities of the components (v _c1, v _c2). The velocity of one or even both components may exceed s ₋. The maximum value of the critical velocity of a given component can be reached when the other component does not move. The approach is generalized for a two-component condensate confined in a cylindrical harmonic potential.      

Critical wind velocity for arresting upwind gas and smoke dispersion induced by near-wall fire in a road tunnel

In case of a tunnel fire, toxic gas and smoke particles released are the most fatal contaminations. It is important to supply fresh air from the upwind side to provide a clean and safe environment upstream from the fire source for people evacuation. Thus, the critical longitudinal wind velocity for arresting fire induced upwind gas and smoke dispersion is a key criteria for tunnel safety design. Former studies and thus, the models built for estimating the critical wind velocity are all arbitrarily assuming that the fire takes place at the centre of the tunnel. However, in many real cases in road tunnels, the fire originates near the sidewall. The critical velocity of a near-wall fire should be different with that of a free-standing central fire due to their different plume entrainment process. Theoretical analysis and CFD simulation were performed in this paper to estimate the critical velocity for the fire near the sidewall. Results showed that when fire originates near the sidewall, it needs larger critical velocity to arrest the upwind gas and smoke dispersion than when fire at the centre. The ratio of critical velocity of a near-wall fire to that of a central fire was ideally estimated to be 1.26 by theoretical analysis. Results by CFD modelling showed that the ratio decreased with the increase of the fire size till near to unity. The ratio by CFD modelling was about 1.18 for a 500kW small fire, being near to and a bit lower than the theoretically estimated value of 1.26. However, the former models, including those of Thomas (1958, 1968), Dangizer and Kenndey (1982), Oka and Atkinson (1995), Wu and Barker (2000) and Kunsch (1999, 2002), underestimated the critical velocity needed for a fire near the tunnel sidewall.     

A wave propagation model for the high velocity impact response of a composite sandwich panel

A solution methodology to predict the residual velocity of a hemispherical-nose cylindrical projectile impacting a composite sandwich panel at high velocity is presented. The term high velocity impact is used to describe impact scenarios where the projectile perforates the panel and exits with a residual velocity. The solution is derived from a wave propagation model involving deformation and failure of facesheets, through-thickness propagation of shock waves in the core, and through-thickness core shear failure. Equations of motion for the projectile and effective masses of the facesheets and core as the shock waves travel through sandwich panel are derived using Lagrangian mechanics. The analytical approach is mechanistic involving no detail account of progressive damage due to delamination and debonding but changes in the load-bearing resistance of the sandwich panel due to failure and complete loss of resistance from the facesheets and core during projectile penetration. The predicted transient deflection and velocity of the projectile and sandwich panel compared fairly well with results from finite element analysis. Analytical predictions of the projectile residual velocities were also found to be in good agreement with experimental data.     

Oxidation dependency of critical velocity for aluminum feedstock deposition in kinetic spraying process

In kinetic spraying process, critical velocity is an important criterion which determines the deposition of feedstock onto the substrate. It has been proven experimentally and numerically that the critical velocity is determined by physical and mechanical properties and the state of materials such as initial temperature and size. In this study, the oxidation effect on critical velocity was investigated using experimental methods. As oxygen content of feedstock increased, critical velocity significantly decreased. In order to find out reasons for difference in critical velocity with oxygen content, individual impact behavior was analyzed and interface microstructure was observed. Due to high brittleness and hardness of oxide, oxide layer on particle influences the particle deformation behavior during impact. And oxide accumulated at interface obstructs the adhesion between activated particle and substrate surface during impact.     

Bounds to Shakedown Loads for a Class of Deviatoric Plasticity Models

The problem of estimating bounds to shakedown loads for problems governed by a class of deviatoric plasticity models including those of Hill, von Mises, and Tresca is addressed. Assuming that an exact elastic solution is available, an upper bound to the elastic shakedown multiplier can be obtained relatively easily using the plastic shakedown theorem. A procedure for computing this upper bound for arbitrary load domains is presented. A number of problems are then examined and it is found that the elastic shakedown factor is given as the minimum of the plastic shakedown factor and the classical limit load factor. Finally, some exact solutions to a number of two dimensional problems are given.     

Prediction of structural response for low velocity impact

The complete modeling for impact on flexible structures can always be done through a three-dimensional finite element model. The FEM approach is often very costly both from modeling and calculation duration point of views, so it can be simplified by using simplified impact models. The selection of an impact model depends on the structural response, thus one should be able to predict the expected structural response a priori in order to select an appropriate impact model. Impact duration is an important parameter that can be helpful for predicting the expected structural response. This paper provides guidelines for the prediction of the structural response on the basis of impact duration and the fundamental period of the impacted structure. A criterion for defining a precise upper limit of low velocity impact is also developed.     

Analytical DSA for Explicit Dynamics of Elastic-plastic Shells

The paper presents an analytical constitutive design sensitivity analysis (DSA) algorithm for explicit dynamics of elastic-plastic finite rotation shells. Two explicit dynamical algorithms for finite rotation shells are presented, and the DSA is developed for the one formulated in terms of the rotation vector and its time derivatives, . The hypo-elastic constitutive model based on the Green–McInnis–Naghdi stress rate is used to derive an incremental algorithm in terms of ‘back-rotated’ objects. The associative deviatoric Huber–Mises plasticity modified by plane stress conditions is implemented in the form suitable for finite rotation/small elastic strain increments. The analytical DSA is developed for the above-specified problem, with the design derivatives calculated w.r.t. material parameters. Design- differentiation of the dynamic algorithm and the scheme of handling the history data and the predicted values in differentiation, which is crucial in computing correct derivatives, are described. Besides, we show how to avoid Newton loops in the DSA algorithm, when such a loop is present in the constitutive algorithm. Numerical examples show that, despite a great complexity of the solution algorithm for the finite-rotation elastic-plastic shells, it is feasible to compute analytical design derivatives of very good accuracy.     

Numerical algorithms and material models for high-velocity impact computations

This article is the written version of a keynote presentation given at the Hypervelocity Impact Symposium in Williamsburg VA in September 2007, in response to accepting the Distinguished Scientist Award from the Hypervelocity Impact Society. As is the tradition, this article is a summary of the technical work performed throughout the career of the award recipient. It covers a range of numerical algorithms and computational material models for high-velocity impact and other intense impulsive loading conditions.     

Experimental and numerical study of ball size effect on restitution coefficient in low velocity impacts

In this article, the Coefficient of Restitution (COR) and Energy Loss Percentage (ELP) of one-dimensional impacts are determined experimentally for different ball sizes using a drop test apparatus. Ball diameters range from 6 to 12 mm, made of steel and aluminum dropped on steel and aluminum sheets.     

Modelling damage evolution in composite laminates subjected to low velocity impact

In this paper, the impact damage of composite laminates in the form of intra- and inter-laminar cracking was modelled using stress-based criteria for damage initiation, and fracture mechanics techniques to capture its evolution. The nonlinear shear behaviour of the composite was described by the Soutis shear stress–strain semi-empirical formula. The finite element (FE) method was employed to simulate the behaviour of the composite under low velocity impact. Interface cohesive elements were inserted between plies with appropriate mixed-mode damage laws to model delamination. The damage model was implemented in the FE code (Abaqus/Explicit) by a user-defined material subroutine (VUMAT). Numerical results in general gave a good agreement when compared to experimentally obtained curves of impact force and absorbed energy versus time. The various damage mechanisms introduced during the impact event were observed by non-destructive technique (NDT) X-ray radiography and were successfully captured numerically by the proposed damage evolution model.     

Viscosity of H<Subscript>2</Subscript>O in the Critical Region

It has been well established that thermodynamic and transport properties of fluids exhibit singular behavior near the critical point. In this article, the theoretical predictions for the enhancement of the viscosity near the critical point are reviewed. It is then shown how these predictions can be used to obtain a representative equation for the viscosity of H₂O in the critical region. Contribution of the National Institute of Standards and Technology, not subject to U.S. copyright.     

Strategies for finding the design point in non-linear finite element reliability analysis

An essential step in FORM, SORM and importance sampling reliability methods is the determination of the so-called design point. This point is the solution of a constrained optimization problem in the outcome space of the random variables, which is commonly solved by an iterative, gradient-based search algorithm. In solving this problem in the context of non-linear finite element reliability analysis, two serious impediments are encountered: (a) for certain material models, the constraint function may have a discontinuous gradient, leading to failure of the search algorithm to converge. (b) The search algorithm may generate trial points too far in the failure domain, where the finite element code fails to produce a result due to lack of numerical convergence. In this paper, remedying strategies are developed for both impediments. The first impediment is addressed by using smooth or smoothed material models, including a smoothed bi-linear model, a Bouc–Wen model and a generalized plasticity model. This is complemented by a proof that sudden elastic unloading does not give rise to gradient discontinuities. The second impediment is addressed by modifying or introducing search algorithms that prevent the trial points from overshooting into the failure domain. Numerical examples are used to demonstrate the two impediments and effectiveness of the proposed remedies.     

A multi-step analysis for determining admissible blank-holder forces in deep-drawing operations

In present investigation a methodology to determine admissible blank-holder forces in deep-drawing operations was established. According to this methodology, the deep-drawing operation is simulated and the maximum blank-holder forces, for stamping friction stir welded tailored blanks, are established based on the comparison of the numerical principal strains fields, obtained in the numerical simulations, with the limiting strains determined analytically for both base materials. Supporting experiments were performed and its results used to confirm the quality of the numerical predictions.     

A model for anisotropic viscoelastic damage in composites

A model for continuous damage combined with viscoelasticity is proposed. The starting point is the formulation connecting the elastic properties to the tensor of damage variables. A hardening law associated with the damage process is identified from available experimental information and the rate-type constitutive equations are derived. This elastic damage formulation is used to formulate an internal variable approximation to viscoelastic damage in the form of a non-linear Kelvin chain. Elastic and viscoelastic equations are implemented into a finite element procedure. The code is verified by comparison with closed-form solutions in simplified configurations, and validated by fitting results of experimental creep tests.     

Microparticle acceleration for hypervelocity experiments by A 3.75MV van de Graaff accelerator and a 100KV electrostatic accelerator in Japan

In-situ dust detectors have been calibrated by dust electrostatic accelerators that can accelerate projectiles to expected mass and velocity ranges of space debris and micrometeoroids. Unfortunately, In Japan, there was no such a facility dedicated to space science research until our research group was established a few years ago. Therefore, we have developed two high voltage accelerators. One is a modified 3.75MV Van de Graaff accelerator operated by High Fluence Irradiation Facility, Research Center for Nuclear Science and Technology, the University of Tokyo (HIT), and the other is a 100kV accelerator dedicated to dust experiment at the Institute of Space and Astronautical Science (ISAS). The particle velocity using the HIT Van de Graaff accelerator is higher than those reported in other accelerator facilities under the same particle mass conditions and encompasses the desired velocity range of micro-meteoroid. Time-Of-Flight dust mass spectrometer and Hybrid dust detector which are under development in Japan have been investigated using HIT dust accelerators. We have also constructed a 100kV electrostatic accelerator designed for easier handling and lower cost operation which is dedicated to dust acceleration, because the HIT Van de Graaff accelerator is being used for ion beam experiments mainly.     

A model for predicting transport velocity in gas fluidized-beds

This study improved the model that used the correlation of the particle entrainment rate to determine the transport velocity. It proposed the new absolute value of the local slope as the criterion of the model for locating the transport velocity in the relationship between dimensionless velocity (U/U_t) and the reciprocal of the entrainment rate (1/K_i¹⁺). It indicated that the criterion depended on properties of fluidized particles and increased with Archemedes number. The Archemedes number was modified by substituting the critical diameter, the maximum particle diameter at which the sum of the interparticle adhesion forces gave a dominant influence to the particle entrainment rate, for the diameter of particles in case that the mean diameter of particles was smaller than the critical diameter. A correlation was suggested to calculate the absolute value of the local slope at the transport velocity. The new model was successful covering the effect of particle properties in predicting the transport velocity.     

Critical Success Factors for New Product Development in Biotechnology Companies

The development of new products has become increasingly critical for the competitiveness of companies, due to increased diversity and variety of products, the reduction of product life cycles, and, primarily, globalization of markets. Thus, the identification and prioritization of critical success factors for developing new products is important, particularly for the high degree of risk and uncertainty involved. The main objective of this article is the identification and prioritization of critical success factors in new product development projects in biotechnology companies in the state of Minas Gerais, Brazil. The research method used was a survey questionnaire, which was sent to a sample of 31 biotechnology companies in Minas Gerais state. The principal findings of this research are that interpersonal skills/relationships of the project leader and technical skills are the most critical factors for successful new product development in this industry. The implications for the biotechnology industry in general, as well as for those responsible for managing new product development, are discussed.